Electrolyte Composition for Inhibiting Thermal Runaway of Battery Cells

The disclosure relates to the field of electrolyte compositions and, more specifically, to inhibiting thermal runaway in lithium-ion batteries.

Lithium-ion batteries (LiBs) are used for various secondary-battery applications. This is particularly due to the high energy density and rechargeability of the LiBs. However, the high energy density and chemistry of LiBs may result in battery cells experiencing thermal runaway events and combustion if the cell is damaged, shorted, or exposed to excessive temperatures. Therefore, there is a need in the art to mitigate and/or inhibit occurrence of thermal runaway events.

Lithium-ion batteries using nickel-rich cathode∥LiSiO(LSO) cells may experience thermal runaway in response to the temperature of the battery cell exceeding a certain temperature. More particularly, nickel-rich cathodes with a layered structure at a charged state may experience a structural collapse at a temperature of approximately 210° C. This collapse generates oxygen radicals, which intensely react with carbonates in the electrolyte. The heat produced by these reactions rapidly drive the temperature of the cell higher. When the battery cell temperature exceed 300° C., further exothermal reactions are triggered by the LSO, which may result in combustion of the battery.

Beneficially, electrolytes in accordance with the present disclosure may be used to mitigate and/or inhibit occurrence of thermal runaway events. These electrolytes may inhibit occurrence of thermal runaway events or mitigate the extent of thermal runaway while providing performance characteristics comparable to or in excess of the performance characteristics of, for example, an electrolyte of LiPF, ethylene carbonate, and ethyl methyl carbonate.

According to aspects of the present disclosure, an electrochemical cell includes an anode, a cathode, and an electrolyte. The anode includes a lithiated silicon oxide material, the cathode includes a nickel-rich material, and the electrolyte is formed from an electrolyte mixture. The electrolyte mixture includes a primary salt, a secondary salt, and a solvent. The primary salt is configured to facilitate ion movement between the anode and the cathode. The secondary salt is a high-HOMO salt. The secondary salt is also configured to form a solid-electrolyte interphase on the anode and a cathode-electrolyte interphase on the cathode. The solvent includes a cyclic solvent component, a linear solvent component, and a fluorinated solvent component.

According to further aspects of the present disclosure, the mixture further includes an additive configured to enhance a solid-electrolyte interface of the anode, the additive being selected from the group consisting of succinic anhydride; vinylene carbonate; tri-methoxymethylsilane; 1,3,2-dioxathiolane-2,2-dioxide; tris(trimethylsilyl) phosphite; and combinations thereof.

According to further aspects of the present disclosure, the high-HOMO salt is selected from the group consisting essentially of lithium difluoro(oxalato)borate (LiDFOB); lithium bis(oxalato)borate (LiBOB); lithium nitrite (LiNO); lithium difluorophosphate (LiDFP); lithium carbonate (LiCO); lithium fluoromalonato(difluoro)borate (LiFMDFB); lithium hexamethyldisilazide (LiHMDS); lithium tetrakis(pentafluorophenyl)borate (LiTPFPB); and combinations thereof.

According to further aspects of the present disclosure, the high-HOMO salt is present in a concentration between 0.05M and 0.5M.

According to further aspects of the present disclosure, the fluorinated solvent component is configured to inhibit side-reactions and consumption of the electrolyte and is selected from the group consisting of fluoroethylene carbonate (FEC); difluoroethylene carbonate (DFEC); trifluoropropylene carbonate (TFPC); 4-((2,2,3,3-tetrafluoro-propoxy)methyl)-1,3-dioxolan-2-one (HFEEC); 4-(2,2,3,3,4,4,5,5,5-nonafluoropentyl)-1,3-dioxolan-2-one (NFPEC) di (2,2,2 trifluoroethyl) carbonate (DFDEC); methyl (2,2,2 trifluoroethyl) carbonate (FEMC); methyl nonafluorobutyl ether (MFE); 1,1,1,3,3,3 hexafluoroisopropyl methyl ether (HFPM); 1,1,2,2 tetrafluoroethyl 2,2,3,3 tetrafluoropropyl ether (F EPE); propargyl 2,2,2 trifluoroethyl carbonate; 2 cyanoethyl (2,2,2 trifluoroethyl) carbonate; 2,2,2 trifluoroethyl allyl carbonate; 3,5,8,10 oxa 4,9 carbonyl 1,1,1,12,12,12 hexafluoro-dodecane; 3,5,9,11 oxa 4,10 carbonyl 1,1,1,13,13,13 hexafluorotridecane; 3,5,10,12 oxa 4,11 carbonyl 1,1,1,14,14,14 hexafluorotetradecane; 3,5,10,12 oxa 4,11 carbonyl 1,1,1,14,14,14 hexafluoro 7 tetradecane; and combinations thereof.

According to further aspects of the present disclosure, the cyclic solvent component includes fluorine and has the following structure:

the linear solvent component includes fluorine and has the following structure:

and each of the R-groups is selected from the group consisting of hydrogen, fluorine, a linear alkyl moiety, a branched alkyl moiety, a linear alkene moiety, a branched alkene moiety, a fluorinated alkyl moiety, and a fluorinated alkene moiety.

According to further aspects of the present disclosure, the primary salt is LiPF6 present in a concentration of 0.5M, the secondary salt is LiDFOB present in a concentration of 0.5M, the cyclic solvent component is a combination of EC and PC, the linear solvent component is DEC, and the fluorinated solvent component is a combination of FEC and DFDEC.

According to further aspects of the present disclosure, the FEC is present in an amount of 15 wt % on the basis of the electrolyte.

According to further aspects of the present disclosure, the electrochemical cell further includes vinylene carbonate (VC) in an amount of 1 wt % on the basis of the electrolyte.

According to further aspects of the present disclosure, the electrochemical cell is formed by hot laminating the anode, the cathode, and a separator using a temperature between 65° C. and 85° C.

According to aspects of the present disclosure, an electrolyte includes a primary salt, a secondary salt, and a solvent. The primary salt is configured to facilitate ion movement between an anode and a cathode. The secondary salt is a high-HOMO salt. The secondary salt is also configured to form a solid-electrolyte interphase on the anode and a cathode-electrolyte interphase on the cathode. The solvent includes a cyclic solvent component, a linear solvent component, and a fluorinated solvent component.

According to further aspects of the present disclosure, the electrolyte further includes an additive configured to enhance a solid-electrolyte interface of the anode, the additive being selected from the group consisting of succinic anhydride; vinylene carbonate; tri-methoxymethylsilane; 1,3,2-dioxathiolane-2,2-dioxide; tris(trimethylsilyl) phosphite; and combinations thereof.

According to further aspects of the present disclosure, the high-HOMO salt is selected from the group consisting essentially of lithium difluoro(oxalato)borate (LiDFOB); lithium bis(oxalato)borate (LiBOB); lithium nitrite (LiNO); lithium difluorophosphate (LiDFP); lithium carbonate (LiCO); lithium fluoromalonato(difluoro)borate (LiFMDFB); lithium hexamethyldisilazide (LiHMDS); lithium tetrakis(pentafluorophenyl)borate (LiTPFPB); and combinations thereof.

According to further aspects of the present disclosure, the high-HOMO salt is present in a concentration between 0.05M and 0.5M.

According to further aspects of the present disclosure, the fluorinated solvent component is configured to inhibit side-reactions and consumption of the electrolyte and is selected from the group consisting of fluoroethylene carbonate (FEC); difluoroethylene carbonate (DFEC); trifluoropropylene carbonate (TFPC); 4-((2,2,3,3-tetrafluoro-propoxy)methyl)-1,3-dioxolan-2-one (HFEEC); 4-(2,2,3,3,4,4,5,5,5-nonafluoropentyl)-1,3-dioxolan-2-one (NFPEC) di (2,2,2 trifluoroethyl) carbonate (DFDEC); methyl (2,2,2 trifluoroethyl) carbonate (FEMC); methyl nonafluorobutyl ether (MFE); 1,1,1,3,3,3 hexafluoroisopropyl methyl ether (HFPM); 1,1,2,2 tetrafluoroethyl 2,2,3,3 tetrafluoropropyl ether (F EPE); propargyl 2,2,2 trifluoroethyl carbonate; 2 cyanoethyl (2,2,2 trifluoroethyl) carbonate; 2,2,2 trifluoroethyl allyl carbonate; 3,5,8,10 oxa 4,9 carbonyl 1,1,1,12,12,12 hexafluoro-dodecane; 3,5,9,11 oxa 4,10 carbonyl 1,1,1,13,13,13 hexafluorotridecane; 3,5,10,12 oxa 4,11 carbonyl 1,1,1,14,14,14 hexafluorotetradecane; 3,5,10,12 oxa 4,11 carbonyl 1,1,1,14,14,14 hexafluoro 7 tetradecane; and combinations thereof.

According to further aspects of the present disclosure, the cyclic solvent component includes fluorine and has the following structure:

the linear solvent component includes fluorine and has the following structure:

and each of the R-groups is selected from the group consisting of hydrogen, fluorine, a linear alkyl moiety, a branched alkyl moiety, a linear alkene moiety, a branched alkene moiety, a fluorinated alkyl moiety, and a fluorinated alkene moiety.

According to further aspects of the present disclosure, the primary salt is LiPF6 present in a concentration of 0.5M, the secondary salt is LiDFOB present in a concentration of 0.5M, the cyclic solvent component is a combination of EC and PC, the linear solvent component is DEC, and the fluorinated solvent component is a combination of FEC and DFDEC.

According to further aspects of the present disclosure, the FEC is present in an amount of 15 wt % on the basis of the electrolyte.

According to further aspects of the present disclosure, the electrolyte further includes vinylene carbonate (VC) in an amount of 1 wt % on the basis of the electrolyte.

According to further aspects of the present disclosure, the electrolyte is configured to be incorporated into an electrochemical cell formed by hot laminating the anode, the cathode, and a separator using a temperature between 65° C. and 85° C.

The above features and advantages and other features and advantages of the present disclosure are readily apparent from the following detailed description of the best modes for carrying out the disclosure when taken in connection with the accompanying drawings.

The following detailed description is merely exemplary in nature and is not intended to limit the application and uses. Furthermore, there is no intention to be bound by expressed or implied theory presented in the preceding introduction, summary, or brief description of the drawings or the following detailed description.

illustrates a schematic battery cell(alternatively referred to as an electrochemical cell), according to aspects of the present disclosure. The battery cellmay be incorporated into a desired battery architecture, such as a stacked, winding, or cylindrical cell architectures. The battery cellincludes a separatordisposed between a pair of electrodes (anodeand cathode). The separatoris configured to electronically isolate the anodeand the cathode. The separatormay be a non-conductive, porous polymeric membrane. The anodeis disposed on a first current collectorand the cathodeis disposed on a second current collector, with each respective current collector being disposed opposite the separator.

The anodeis configured to intercalate ions while the battery cellis charging and de-intercalate ions while the battery cellis discharging. The anodeincludes an electroactive material, such as a lithiated silicon material. In some aspects, the lithiated silicon material has a general formula of LiSiO, where y is between 0 and 1 and x is between 0 and 2. In certain aspects, the lithiated material is a lithiated silicon-rich oxide, where x is less than 1. The lithiated silicon material may have a suitable morphology selected from the group consisting of nanoparticles, nanofibers, nanotubes, microparticles, combinations thereof, and the like.

The anode may further include a carbon material to enhance characteristics of the anode. For example, the carbon material may be selected to promote a particular morphology of the lithiated silicon material, enhance ion intercalation and deintercalation, optimize mechanical properties of the anode, combinations thereof, and the like. The carbon material may be selected from the group consisting of graphite, hard carbon, or soft carbon.

A suitable amount of lithiated silicon material is present in the anode. In some aspects, the lithiated silicon material is between 5 wt % and 80 wt % of the anode. In certain aspects, the lithiated silicon material is between 5 wt %-30 wt % of the anode. The anodeis loaded to provide optimize operating characteristics of the battery cell. In some aspects, the anodeis loaded to a capacity between 4 mAh/cmand 8 mAh/cm. In certain aspects, the anodeis loaded to a capacity between 4.4 mAh/cmand 5.5 mAh/cm.

The cathodeis configured to intercalate the ions received from the anodewhen the battery cellis discharging and de-intercalate the ions for transport to the anodewhile the battery cellis charging. The cathodeincludes an electroactive material that is cooperative with the electroactive material of the anodeto facilitate ion flow and electron flow between the anodeand the cathode. The electroactive material of the cathode may be a transition-metal electroactive material, such as a nickel-rich material (e.g., >60% nickel). In some aspects, the nickel-rich material is selected from the group consisting of LiNiO(LNO), Li[NiCoMn]O(NCM), Li[NiCoAl]O(NCA), Li[NiCoMnAl]O(NCMA), combinations thereof, and the like. In certain aspects, the nickel-rich material is selected from the group consisting of NCMA.

The first current collectorand the second current collectorare configured to collect and distribute free electrons from and to the adjacent anodeand cathode. The free electrons are moved between the first current collectorand the second current collectorvia an external circuit. The external circuitmay include an external devicewhich may be a load that consumes electric power from the battery celland/or a power source that provides electric power to the battery cell.

Each of the anode, the cathode, and the separatormay further include an electrolyte. For example, pores of the anode, the cathode, and/or the separatormay be infilled with the electrolyte. The electrolyteis formed from an electrolyte solution and promotes movement of ions between the anodeand the cathodeduring charging and discharging of the electrochemical cell.

The electrolyte solution includes a primary salt, a secondary salt with a high highest occupied molecular orbital (a high-HOMO salt), and a solvent mixture including a fluorinated solvent. While not being bound by theory, it is believed that electrolyte solutions described herein optimize performance of the battery cellby enhancing a solid-electrolyte interface (SEI) formed on the anode material, enhancing a cathode-electrolyte interface (CEI) formed on the cathode material, preferentially trapping generated oxygen radicals prior to their reaction with carbonate solvents, and inhibiting combustion and/or thermal runaway though gasification of the fluorinated solvent.

The primary salt is configured to configured to facilitate ion movement between the anodeand the cathode. The primary salt may be, for example, a lithium salt. In some aspects, the lithium salt may be selected from the group consisting of lithium hexafluorophosphate (LiPF); lithium difluorosulfimide (LiFSI); lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); combinations thereof; and the like. In certain aspects, the primary salt is LiPF. The primary salt may be present in a concentration between 0.5M and 4M. In some aspects, the primary salt is present in a concentration between 0.5M and 1.2M. In certain aspects, the primary salt is present in a concentration of 0.5M.

The high-HOMO salt is selected to include an energy level of the HOMO that is sufficiently high to inhibit side reactions of the electrolyte solvents. These side reactions, such as the interaction between carbonate solvents and oxygen radicals, inhibit performance of the battery cell. For example, when a nickel-rich cathode is at charged state, structural collapse may occur if exposed to an elevated temperature (˜210° C.). The structural collapse generates oxygen radicals, which will intensely exothermically react with one or more carbonate components of the electrolyte. Beneficially, the high-HOMO salt acts to enhance the CEI formed by the electrolyte, to inhibit thermal runaway of the battery cellby preferentially trapping oxygen radicals generated in the battery cell, which inhibits the occurrence of more vigorous and/or more exothermic reactions of the oxygen radicals with the carbonates in the electrolyte, and/or to enhance the SEI formed by the electrolyte.

In some aspects, the high-HOMO salt maybe selected from the group consisting of lithium difluoro(oxalato)borate (LiDFOB); lithium bis(oxalato)borate (LiBOB); lithium nitrite (LiNO); lithium difluorophosphate (LiDFP); lithium carbonate (LiCO); lithium fluoromalonato(difluoro)borate (LiFMDFB); lithium hexamethyldisilazide (LiHMDS); lithium tetrakis(pentafluorophenyl)borate (LiTPFPB); combinations thereof; and the like. In certain aspects, the high-HOMO salt is LiDFOB.

The high-HOMO salt may be present in a concentration that is less than or equal to the primary salt. In some aspects, the high-HOMO salt is present in a concentration between 0.05M and 0.5M. In certain aspects, the high-HOMO salt is present in a concentration between 0.1M and 0.5M. In certain further aspects, the high-HOMO salt is present in a concentration of 0.5M.

The solvent mixture includes a cyclic solvent component, a linear solvent component, and fluorinated solvent component. The solvent mixture is configured to maintain the primary salt and the secondary salt in a generally homogenous solution throughout the battery cell, to participate in formation of the SEI and CEI, and to provide a desired viscosity of the electrolytefor a predetermined range of operating temperatures.

The cyclic solvent component is configured to participate in the formation of a stable SEI by promoting formation of lithium alkyl carbonates on the surface of the anode material. While not being bound by theory, it is believed that the cyclic solvent component or another cyclic solvent component may be configured to participate in the formation of a stable CEI on the surface of the cathode material.

The cyclic solvents may be selected from the group consisting of ethylene carbonate (EC); propylene carbonate (PC); γ-butyrolactone (γBL); 5-(3′,4′-dihydroxyphenyl)-γ-valerolactone (γVL); 4-methylmorpholine 4-oxide (NMO); combinations thereof; and the like. In some aspects, the cyclic solvent component is a combination of EC and PC. In some aspects, the cyclic solvent is present in an amount of between 10 wt % and 40 wt %. In certain aspects, the cyclic solvent is present in an amount of between 20 wt % and 30 wt %.

The linear solvent component is configured to optimize fluidity of the electrolyteto optimize ion transport and operating temperature ranges for the battery cell. The linear solvent component may be a cyclic carbonate. In some aspects, the linear solvent component may be selected from the group consisting of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethyl acetate (EA), n propyl acetate (nPA), i-propyl acetate (iPA), n-butyl acetate (nBA), i-butyl acetate (iBA), methyl propionate (MP), methyl butyrate (MB), methyl formate (MF), ethyl formate (EF), n-propyl formate (nPF), i-propyl formate (iPF), n-butyl formate (nBF), i-butyl formate (iBF), dimethyl formamide (DMF), dimethyl ketone (DMK), methyl ethyl ketone (MEK), acetonitrile (CAN), propionitrile (PN), n-butyronitrile (nBN), i-butyronitrile (iBN), combinations thereof, and the like. In certain aspects, the linear solvent component is selected from the group consisting of EMC, DMC, DEC, a combination thereof, and the like. In certain further aspects, the linear solvent component is DEC. The linear solvent may be present in an amount of between 60 wt % and 90 wt %. In some aspects, the linear solvent is present in an amount of between 70 wt % and 80 wt %.